Light-sensitive cell manufacture



March 23, 1937. c. s. TR'EACY 2,074,676

LIGHT SENSITIVE CELL MANUFACTURE FnedMaroh es, 1935 BY .Zan/AY ATTORNEY Patented Mu. '23, 1931 UNITED. sTATEs PATENT oFF-lcs 2.0mm i uon'r-saNsmvr: om mancuernas Application March 8, 1935, Serial No. 9,584

11Claima.

5 separated into two electrodes by a sinuous trace.

Selenium, or similar light-sensitive material, is sublimed onto and bridges the gap between the adjacent electrode portions,

The present invention relates to an improved process for depositing by sublimation, selenium or similar light-sensitive material on the interdigitated electrodes or grid.

Selenium occurs in several allotroplc forms having different degrees of photo-sensitivity. In subliming selenium, it is desirable to insure, not only that the right kind of crystals are formed on the electrodes, but also that a ilne grain deposit of selenium or the like be obtained on the electrodes or grid, as the ner the grain, the more uniformly opaque or dense is the deposit. Also, a finer grain adheres better to the electrodes, which apparently accounts for lower cell noise when using the cell for reproducing sound from sound film.

In my application, Serial No. 9,585, filed March 6, 1935, I have disclosed and claimed certain features disclosed herein for the temperature control of crystal growth to insure that a particular allotropic form which is photo-sensitive will be crystallized on the electrodes or grid. The present invention relates to a process for insuring thatI crystals of small size will be obtained.

I have discovered that the grain of the deposit is not as ilne when the grid is subjected to selenium vapor for the first time as it is if the initial deposit is removed, forV example, by scraping it oi the grid with a dull knife, and a second de-` posit sublimed on the grid. The second deposit also forms more uniformly, and in a shorter time, which is conducive to smaller crystals. The deposition and removal of the crystals are repeated several times, such as six times, with the result that the final coating is deposited uniformly in a short time and with an evenlayer of crystals so small that the individual crystals are only visible when viewed with a high power objective lens.

Prior to the final deposit, and after the preceding deposit has been scraped away, the metallic electrode surface has been examined, with the result that no visible change in the electrode surface is brought about by the crystallizations and scrapings, the surface appearing smooth even when enlarged four hundred' times. In some 55 way which is not understood, the removal of the crystalline deposit from the grid serves to sensitize the grid surface and facilitate a subsequent deposition of crystals.

For further details of the invention, reference may be made to the drawing, wherein:

llg.` l is a side elevation, partly in section, of a furnace which may be employed for subliming selenium or the like onto the electrodes of the cell according to the invention.

Fig. 2 is a perspective view of the furnace of Fig. l with the furnace open.

Fig. 3 i's a perspective view of a cell element onto which the selenium or the like may be sublimed according to the invention.

A cell element I9, onto which the light-sensitive material is to be sublimed, is shown in Fig. 3, wherein the glass' support l, has the interdigitated electrodes or grid 2, 3. This grid 2, 3 may be made as follows, or otherwise:

Preferably, the glass support i for the grid 2, 3 is soft glass. v'I'he glass support i is coated withametallicsolution, such as a colloidal mixture of two parts of platinum chloride and one part of gold chloride, and red in a munie furnace not shown. In some cases, the surface of the fused metallic layer on the glass may be uneven or warped, dueto raisingv the soft 'glass to a temperature high enough to fuse the metal to it. In other cases, the grid blank is not warped. Preferably, the metal layer is pre-red to a temperature below the fusion point. After cooling, the hard coating on the metal is dissolved in water, the sinuous trace l, which may be 1 or 2' mils wide, is then cut, and thereafter the grid 2, 3 is red to a temperature to fuse the metallic grid 2, 8 to the glass I, as described and claimed in my co-pending application, Serial No. 9,583, led March 6, 1935.

'I'he element i0 is now ready to have selenium or the like sublimed on it according to the present invention, and for this purpose, use may be made of a furnace 'such as shown in Figs. 1 and 3. This furnace comprises a hot plate 5, which supports the cell elements I0, and a second hot plate 6, which carries a molten pasty layer 1 of the selenium or other light-sensitive material to be sublimed onto the elements I0. 'I'he plates 5 and 5 are hinged at 9 whereby the upper plate 6 overlies the bottom plate 5 when the oven is closed, as in Fig. 1, these plates being held apart by a distance of the order of inch to M; inch, this distance of course being determined by the height of the insulating spacer 9. The plate 5 is provided with a thermometer il, an electric heater i2 and a thermostat generally indicated at I3. The

upperplaslsnmnariyproviaeawnhatnerter I4, an electric heater Il, and a thermo-iA controlindicatedatll. Whenthefurnace inlfig.3isfullyopened,the sublimingsurfaceHshorisontaLandinthisposi--- tion, it is lplinkled, while hot, with a thin coatingy of the subliming mixture which may, for example, comprise 19 parts of pure powdered selenium should have a temperature of about 245 C. or

higher, preferably 295 C., whereby the subliming mixture meltsto'formapastrycoatingonsurface l as indicated at 1.- The furnace is now closed as shown in lig. 1, the lower plate l being maintained by thermostat Il at a temperature such that the elements II are kept below the melting point of the subliming mixture 1, while the temperature oftheupperplateorsubliming'sm'facel isregulated by thermostat I4 toatemperature such that a heavy concentration of vapor from mixture 1 is provided for coating the elements III.

The lower plate l is provided with a series of apertures I1 at opposite sides thereof. 'Ihese apertures II in effect provide vanes to cool the lower plate 5' and prevent its temperature from rising above the desired value due to its proximity to the upper plate 6.

For the initial sublimed coating, the subliming surface l is regulated at a temperature of 245 C. or higher, preferably 295 C., depending on the desired rate of evolution of vapor, and the lower plate 5 is regulated to a temperature of 140 to 145 C., whereby the elements Il receive the vapor at the correct 'temperature for the growth of the particular allotropic form which is photo-sensitive. The feature of temperature control to control crystal growth is disclosed and claimed in my copending application, Serial No. 9,585, filed March 6, 1935. The sublimation lproceeds lfor about one to one and one-half hours and results in a soft sublimed coating which is easily scraped oil the elements Il. When the elements III are fairLv well coated, as they will be under the conditions above mentioned, they are removed from the furnace and scraped with a dull knife to thoroughly remove the sublimed coating on the electrodes 2, I. If the elements I9 are iiat,'a fiat scrapermaybeused; iftheyarewarpedasshown in Fig. 2. a curved scraper is used. The scraped elements Ilarereplacedinthefurnaceandagain the mixture I is sublimed on them, whereupon the sublimed coating is again scraped' ofi. 'fhe steps of coating and scraping are repeated five or six times. the time of coating being successively reduced as the formation of a subsequent layer is hastened by the former crystallizatlon of sublimations. After the selenium has been deposited and scraped away about six times,'the grid surface is thoroughly cleaned with a jeweler's brass bristle brush, or the like, to remove all visible portions of the sublimed material, and the final coating of the selenium mixture is sublimed on the grid element Il.

The nal coating is always done with a fresh.

eraliy suilicient to deposit a non-transparent closely adherent and fine grained deposit.

Ai'terv removing the grids Il from the furmce. thedepositof sublimedmaterialonthesurfaceof the electrodes 2. l, outside of the grid 4, isscraped away and two drops of a dilute solution of iodine in carbon disulphide is used to wet the deposit. The iodine possibly .reacts with traces of oxide present to reduce it to selenium and telluriuln. Excess iodine forms selenium and tellurium iodide which tends to decompose, and lalso to sublime away, and care must therefore be taken not to use too much. This treatment apparently produces cells with better signal to noise ratio.

Subsequent annealing' of the coated grids is not necessary, as the desired photo-sensitive form of the light-sensitive material is originally formed onthegridaduetomaintainingthelowerplate 6 at the temperature necessary for the desired crystal growth.

Aprotectivegiasscapiscemented overthetrace 4, the excess selenium around the cap is removed. and the element mounted. for example, as shown and claimed in the application to Carpenter et al.. Serial No. 747,610, led October 9, 1934, for "Light-sensitive cell", or as in the patent toLyon, #1,948,766.

I claim:

1. 'f'hemethodofobtainingannegrainopaque coating of selenium on separated electrodes which comprises maintaining said electrodes .at an elevated temperature favorable for the formation of photo-sensitive crystals while directing vapor of selenium thereon for a certain time, removing the material thus deposited on said electrodes, and thereafter maintaining said electrodes at said elevated temperature, while directing vapor of selenium thereon for a shorter lime.

2. The method -to claim l. wherein said mst-mentioned directing of vapor continues for a period of the order of an hour. and said last-mentioned directing of vapor continues for a period of the order of a few minutes.

3. The method of obtaining a fine grain opaque coating of selenium on separated electrodes which comprises maintaining said electrodes at a temperature of about to 145 C., while directing selenium vapor thereon at a certain rate for a -face and removing the selenium thus sublimed.

5. 'I'he method according to claim 4 which comprises eifecting said removing by scraping.

6. 'I'he method of coating selenium on separated electrodes which comprises sensitizing said electrodes by maintaining said electrodes at an elevated temperature favorable for the formation of photo-sensitive crystals while directing vapor of selenium thereon for a certain time and removing the selenium thus deposited:land thereafter directing vapor of selenium on said electrodes.

7. The method accordingto claim 6 wherein said last mentioned directing of selenium vapor is eifected while maintaining said electrodes substantially at said elevated temperature.

8. 'I'he method according to claim 6 which comprises repeating said sensitising prior to said last step of directing seleniumvapor on said electrodes.

9. The method according to claim 6 which comprises edecting said removing by scraping.

10. The method of coating selenium on sepay rated electrodes which comprises sensitixing said is electrodes by maintaining said electrodes' at nn elevated temperature favorable for thev formation of photo-sensitive crystals 'while vapor of selenium thereon for a certain time and scraping the selenium thus deposited: repeat- 10 ing said sensitising, and thereafter directing vapor of fresh selenium on said electrodes while maintaining said electrodes subnantially at said elevated temperature.

11. 'I'he method of coating selenium on a sur- CERTIFICATE OF CORRECTION.

Patent No. 2,074,676.

March 23, 1937.

CYRIL s. TREACY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: first column, line 13, for "pastry" read pasty; and second column, line Page 2,

P5l claim 1, for "material" read Selenium; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of May, A. D. 1937.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

9. The method according to claim 6 which comprises edecting said removing by scraping.

10. The method of coating selenium on sepay rated electrodes which comprises sensitixing said is electrodes by maintaining said electrodes' at nn elevated temperature favorable for thev formation of photo-sensitive crystals 'while vapor of selenium thereon for a certain time and scraping the selenium thus deposited: repeat- 10 ing said sensitising, and thereafter directing vapor of fresh selenium on said electrodes while maintaining said electrodes subnantially at said elevated temperature.

11. 'I'he method of coating selenium on a sur- CERTIFICATE OF CORRECTION.

Patent No. 2,074,676.

March 23, 1937.

CYRIL s. TREACY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: first column, line 13, for "pastry" read pasty; and second column, line Page 2,

P5l claim 1, for "material" read Selenium; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of May, A. D. 1937.

(Seal) Henry Van Arsdale Acting Commissioner of Patents. 

